1. Field of the Invention
The instant invention is directed to a piercing punch and ejector assembly. More particularly, the instant invention is directed to a piercing punch and ejector assembly charaterized by increased operating life, reduced downtime and maintenance requirements and simpler design than the assemblies of the prior art.
2. Description of the Prior Art
Piercing punch and ejector assemblies are fundamental tools employed in the machining and material forming arts. These assemblies include a piercing punch member which cuts out a slug or blank and an ejecting means member which insures that the cut out slug or blank does not adhere to the cutting edge face of the piercing punch member.
Typically, piercing punch and ejector assemblies have included a spring actuated ejecting pin disposed in a bore provided in the point thickness section, or beyond, of the piercing punch member. A spring, situated in a counterbore in the body and shoulder thickness sections of the punch member, urges the ejection pin outward beyond the surface of the cutting edge of the punch member.
Although these designs function to punch slugs or blanks from working stock they present important design, operation and maintenance problems to workers in this art. This has resulted in the development of improved designs to overcome these perceived defects. However, these designs still retain an ejection pin. Since, there are certain inherent limitations in the utilization of spring activated ejector pins, no number of design changes can completely overcome these shortcomings.
One of these design limitations is the requirement that the bore and counterbore, required to accommodate the ejection pin, the spring and additional means necessary to hold the pin and spring in place, i.e., a set screw, a collar and the like, extends longitudinally from one end of the punch member to the other, from the cutting edge to the top of the shoulder. This "through hole" effectively makes the piercing punch member a tubular instrument. Obviously, a tubular punch is a weaker tool than the same punch constructed substantially solid. This defect is even further accentuated by the larger diameter counterbore employed to accommodate all ejector means constituents other than the ejector pin. The result of this design flaw is a punch member having a shorter working life than the same piercing punch member having a more solid construction.
Although of lesser significance, the above discussion suggest a secondary disadvantage of the through hole design of the prior art. That is, this design requires the machining of a pair of holes, a bore of smaller diameter, and a counterbore of larger diameter. This design requirement adds complexity and expense to the manufacture and cost of the piercing punch member.
Another limitation of the typical piercing punch and ejector assembly of the prior art is the difficulty associated with disassembly of the ejector means during the periodic sharpenings of the cutting edge of the piercing punch member. This periodic sharpening is necessary to extend the life of the punch member. During this sharpening the ejector means, disposed in the bore and counterbore of the punch member, is removed. The removal and reinsertion of the ejector means requires total disassembly of the punch and die apparatus in that access to the counterbore end of the punch is required.
It is appreciated that ejector pin designs have been advanced that eliminate much of the difficulty involved in removal of the ejector means. Specifically, ejector pin designs have been developed in which only the ejector pin is removed, and thereafter reinstalled, during sharpening. In other designs, the ejector pin is held in the retracted position during sharpening. However, to provide this simplification in maintenance, a complex ejector means design must be employed. This adds significant complexity and cost to the punch and ejector assembly. Thus, the use of an ejector pin in a piercing punch and ejector assembly requires time consuming and labor intensive maintenance cost or, in the alternative, a highly complex and expensive design.
The complexity and expense of typical through hole designs is also evidenced by the need of these designs of the prior art to include a hole disposed normal to the bore or counterbore that provides venting. Without going into detail, suffice it to say, that the ejecting means employed in through hole designs create vacuum effects at the cutting edge of the punch member which requires this expensive remedy. Of course, the absence of such an expedient results in operating malfunctions resulting from the cut out blank adhering to the punch due to this vacuum effect.
A related problem, associated with the sharpening of piercing punch members, in the prior art is the limitation on the number of times the punch member may be rehoned before the punch member is discarded. Each time the punch member is resharpened its length is correspondingly decreased. Although this has no adverse effect on the typical ejector pin design in the unrestrained position, since it only causes the pin to extend further beyond the cutting edge surface, it has a very deleterious effect on the punch and ejector assembly in the retracted position. After enough resharpenings there is an insufficient length of bore to accommodate the ejector pin when the ejector means spring is compressed and the ejector pin retracted. Since ejector pins are manufactured in standard lengths, a new shorter pin cannot replace the original longer pin with the result that the whole assembly must be replaced.
In summary, the piercing punch and ejector assemblies of the prior art suffer from limitations in terms of their strength of construction, their difficult and time consuming maintenance requirements or complex and expensive design, and their limited effective working life.